What are emulsions?
A subset of the larger group of two-phased systems, emulsions is the term usually given to a liquid system of two immiscible liquid (liquids that don’t mix together) phases, in which one phase is dispersed in the other. An emulsion is formed when two immiscible liquids are mixed together through vigorous shaking. The process of making an emulsion is known as emulsification.
Emulsion is derived from the Latin word ‘mulego’, which means ‘to milk’. Milk itself is a naturally occurring emulsion; a dispersion of fats and water. Other natural emulsions are egg yolk, butter and mayonnaise.
Put simply, an emulsion is basically a mixture of liquids that doesn’t entirely ‘mix’ completely.
Examples of Emulsions
Oil and water mixtures, one of the most common examples, are emulsions when shaken together.
Egg yolk is an emulsion containing the emulsifying agent lecithin.
Crema put on espressos and coffees is an emulsion of water and coffee oil.
Butter is an emulsion of water and fat.
Mayonnaise is an oil-in-water emulsion, with lecithin in the egg yolk stabilizing the emulsion
The negative reel of photographic film is layered with an emulsion of silver halide in gelatin.
Types of Emulsions
Emulsions can be classified into two types.
Oil-in-water: If the aqueous phase is the continuous phase and the oil phase is dispersed, then it’s an oil-in-water emulsion.
Water-in-oil: If the aqueous phase is immersed in the continuous oil phase, then it is a water-in-oil emulsion.
The kind of emulsion that results due to mixing of two liquids is largely dependent on the type of emulsifier used and the volume of the two liquids.
Emulsions are unstable. The two liquid phases do disperse in each other when shaken, but most emulsions won’t stay that way for long. If an emulsion is left to rest, it will start to disintegrate. This is called ‘cracking of emulsion’ or ‘phase inversion’. To stop the emulsion from breaking apart, emulsifiers or emulsifying agents are used.
Instabilities of Emulsions
The ability of an emulsion to retain its form is called its stability. Most emulsions aren’t stable unless an emulsifier is added to the mixture. There are three common types of instabilities that occur in emulsions.
Flocculation occurs when the droplets of the immersed phase flock together due to attractive forces between them and aggregate together.
When the droplets of the discontinuous phase stick together and combine to form a bigger drop of the discontinuous phase, it is called the coalescence.
Creaming is when the droplets rise to the top of the continuous phase and settle there, forming a layer of the discontinuous phase.
To ensure that the emulsions don’t fall apart, emulsifiers are added to the mixture that makes the emulsion retain its state.
Other Properties of Emulsions
Emulsions usually appear cloudy or white, because of the non-uniform scattering of light off the phases. If all light is scattered equally, the emulsion will appear white, while diluted emulsions can take on a bluish tinge. If particle sizes are too small, the emulsions might even take on a translucent appearance.
Two liquids can form different types of emulsions. Like water in oil or oil in water. They can even form more complex emulsions, like oil-in-water-in-oil.
What Are Emulsifiers?
Emulsifiers, also called emulgents and emulsifying agents, are chemical additives that are added to emulsions to ensure their stability. So, for example, in a mixture of oil and water, the two phases start to separate once the mixture is left sitting. When an emulsifier is added to this solution, the phases remain dispersed and a stable emulsion is obtained.
How Does an Emulsifier Work?
There are three mechanisms at work that guarantee that the emulsifying agent does its job of increasing stability in an emulsion. The science behind the process banks on three theories.
Surface Tension Theory
This theory states that the emulsifier keeps the emulsion stable by reducing the interfacial surface tension between them, stopping the two phases from separating from one another.
The emulsifier forms a thin film over one of the phases, which makes the globules repel each other and ensure consistent dispersion and suspension.
Some emulsifiers alter the viscosity of the suspension medium enabling the non-continuous phase to remain immersed in it.
Types of Emulsifiers
Some of the most common natural emulsifiers available are
Egg yolk – in which the main emulsifying agent is lecithin.
Mustard – where a variety of chemicals in the mucilage surrounding the seed hull act as emulsifiers
Soy lecithin is another emulsifier and thickener
Pickering stabilization – uses particles under certain circumstances
Mono- and diglycerides - a common emulsifier found in many food products (coffee creamers, ice-creams, spreads, breads, cakes)
Sodium stearoyl lactylate
DATEM (diacetyl tartaric acid esters of mono- and diglycerides) – an emulsifier used primarily in baking
Simple cellulose – plant-derived emulsifier
Use of Emulsifiers
Emulsifiers are used for a wide range of purposes across a variety of industries.
Emulsifiers in Food Industry
The first emulsifier ever used in the food industry was probably egg yolk. Egg contains the emulsifying agent lecithin, which became the primary emulsifier used in foods. Because of its short-life, people shifted to using lecithin derived from soy beans.
As science advanced, people discovered emulsifiers, called mono- and di-glycerides , which were derived from fatty acids. These natural emulsifiers along with polysorbate 65, Polysorbate 60 and sucrose ester are used in the manufacturing of salad dressings, breads, ice creams, chocolate, margarine, and a variety of different everyday foods.
The legislation surrounding the use of emulsions is very strict in the food industry. The emulsions used should be purified natural products or synthetic emulsifiers that have similar chemical structures to natural products.
There are other considerations to take into account too, for example whether the emulsifier is vegan, kosher or halal.
Emulsifiers in Cosmetic Industry
Cosmetic products such as lotions, creams and serums are in fact emulsions.
They require essential oils and water to be mixed, but they cannot do so without an emulsifier. Most of the scenting in our cosmetics is also achieved through mixing fragrant oils with the products.
The first emulsifier used in the cosmetics industry was probably beeswax by the Ancient Greeks, which was and is still added to many cosmetic and skincare products because of its emulsifying and hydrating properties.
Both type of emulsion, oil-in-water and water-in-oil are very important in making cosmetics and skincare products. The water-in-oil emulsions are utilized for night screams, sunscreens and body lotions. Since the oil is the first to touch the skin, these products are heavy and greasy, as they are intended to be.
Oil-in-water emulsions are used for light-weight products like day creams, toners and serums.
Care must be taken about which emulsifiers are used for what purpose. Some emulsifiers can prove irritating to the skin and should be avoided.
Emulsifiers in Pharmaceutical Industry
Emulsifiers are widely used in the pharmaceutical industry in the production of ointments, medicated gels, creams, and suspension syrups. These products usually contain water as a starting material to which a chemical with medicinal properties is added. An emulsifier is stirred into the mixture to prevent the two from separating. Emulsifiers also help to increase the shelf life of products.
Micro emulsions are in delivering vaccines and eliminating microbes. Safe emulsifiers need to be used for injecting into the body. The most typical emulsifier used in administering shots and vaccines is soybean oil, whose particles are tiny enough to merge with the lipids and other fluids to kill pathogens, protecting the body against diseases. Nano-emulsion, like the ones in soybean oil, also does not harm human cells.
Emulsifiers are also extensively used in the paint industry, for firefighting and for chemical synthesis.
There are several types of emulsifiers available. However, there are certain things that should be considered before deciding on what emulsifier would suit you or your product best.
Natural or Synthetic
For purposes of ingestions and skin application, it is probably best to go with a natural emulsifier. The tricky part is, how natural can it be? Even lecithin, an emulsifying agent derived from egg yolk, and other plant-based emulsifiers go through a lot of chemical processing before they are ready to be used in any product. Emulsifiers are extracted and processed, and this is how close you get to a natural emulsifier.
Synthetic emulsifiers like PPG and PEG, however even sounds distasteful to use in organic products r products that directly go into or on your body. Synthetic emulsifiers can be perfectly appropriate for mixing in paints and fire extinguishing liquids, but they should be avoided in cosmetic and oral products.
You should be careful and responsible for the emulsifiers you use, especially in products that are ingested. Some emulsifiers are derived from foods and plants, or might contain traces of products that are forbidden in some religions and societies. If selling a food item to a largely Muslim market, select the emulsifier that is Halal. For Jews, make sure the emulsifier is kosher, and for vegans choose emulsifiers that are largely plant-based. There are E-numbers assigned to each additive, which describe its origins.
Determine the desired viscosity of your product, and choose an emulsifier accordingly. In the end, there is no perfect emulsifier. It depends on what you are using it for and the desired characteristics in your end product. If you’re making a heavy body lotion, you will require an emulsifier that gives you the thickness. If you’re in search for an emulsifier for making a light toner, you might have to choose differently. Not all emulsifiers give the same results.
Cold and Hot Process
Most emulsifiers come in the form of powders or pellets that would need to be melted in the solution. This can be troublesome if you’re working with heat sensitive materials. There are some that are available in liquid form too. Research and find what emulsifier would work best for you. If you’re already working with materials that would need to be melted for the end product to e made then it is pointless to use a cold process emulsifier, which are comparatively hard to come by.
Need of Stabilizer or Co-emulsifiers
Some emulsifiers aren’t enough on their own; they need another emulsifier or a stabilizer to give the desired results. The situation typically arises with working with alcohol or achieving the ideal viscosity. In such a case, it would neither be convenient nor feasible for you. Be very clear about the results you’re after, and choose an emulsion that is the perfect fit for your product.
Thus, you see, there is no ‘best’, standard emulsifier to use. The perfect emulsifier will vary across different industries and products. Maverick Oils stocks a variety of emulsifiers that you can look up and order according to your needs.